1. Field of the Invention
This invention relates to water heaters or boilers and in particular to means for reducing a failure caused by heating repeatedly above the ductile to brittle transition temperatures.
2. Background Information
Water heaters and boilers typically have a water heater tank, often of the vertical or horizontal tube type which utilizes fire tubes located above a combustion chamber.
In some water heaters or boilers, a fossil fuel power burner is used in the combustion chamber. The tubesheet which separates the combustion chamber from the water is heated by the burning fossil fuel to a relatively high temperature and then cooled when the burner in the combustion chamber is turned off. The tubesheet and water are heated and then cooled repeatedly over a long duration in the life of the water heater or boiler. As a consequence, the tubesheet is heated and cooled repeatedly to temperatures above the ductile to brittle transition temperature and then cooled below this temperature. The result of this repeated heating and cooling above and below the DPTT eventually causes the metal to lose its ductility, become brittle or crystalline and ultimately fail, allowing the discharge of the water and sediment in the water heater or boiler.